The props designed for the movie Aliens are amazing. It helped pull you into the world, and set it apart from other movies.

M41A Pulse Rifle

M56 Smart Gun

M240 Flamethrower

Motion Tracker

HK VP-70 Pistol

S&W Model 39
Both the HK VP-70 and S&W Model 39 are real pistols. The HK VP-70 is considered the first polymer frame pistol (in 1970, long before Glock). The S&W Model 39 has been around a long time, and was used in Vietnam by the US military in concert with a silencer for special operations.

Colonial Marines Carrier Sulaco

Colonial Marines Dropship

Colonial Marines APC
The most badass APC of all time. I still want one.

and an escape vessel
The movie begins with a long scene showing the vessel from the outside first, and then the inside. This was a very good ship prop, and the set inside matched the industrial look of the ship on the outside.

Pistol
Kane had one of these in his hand when he was exploring the mysterious derelict ship. I wondered why they never tried using it on the alien.

Flame Thrower
One of my favorite movie weapon props. Flame throwers are actually very dangerous weapons to the user, and extremely dangerous weapons to have aboard a space vessel. But it looked real cool, and that's all that counts.

Harpoon Gun
Ripley would use anything to kill an alien. Including this harpoon gun.

Ash

Alien
It really doesn't get much scarier than this. It rips out of your fucking body, and grows to full size in less than twelve hours.

AT-AT Walker
Who doesn't remember the Invasion of Hoth with the massive, slow moving AT-AT walkers? Seeing these for the first time made me fear the wrath of the Empire! Such amazing vehicles, and one of the greatest scenes in movie history.

BlasTech E-11 Blaster Rifle
This is the preferred weapon of the Imperial Army, and is seen all over the Star Wars universe. Modified from a Sterling L2A3 submachine gun, this gun was used throughout the Star Wars Trilogy.

Bat'leth
This badass melee weapon was the preferred weapon of duels and personal vendettas. Throughout the 80's and 90's Star Trek shows, it was shown to be a Klingon's most prized possession, aside from his personal honor.

D'k Tahg
Otherwise known as a knife, this weapon is hard to pronounce, but seems to be a preferred weapon among Klingons for settling personal disputes. There are other knives that the Klingons use, but this one is the most iconic.

Auto9 (Beretta 93R)
This was one of the coolest things about the movie to me when I watched this as a kid. I wanted one of these so bad. Of course, no real gun has unlimited ammo like they do in the movies. This is a heavily modified Beretta 93R automatic pistol. Modified 93R's are also used in other sci-fi movies, like Equilibrium, and Underworld.

Director Paul Verhoven is well represented in this list, as this is the third one of his movies making it to this list. I wish I could show you the ships as well, but those pictures are harder to acquire.

Morita MK rifle
One cool aspect of this rifle is that it comes with an underslung shotgun. Rico uses the shotgun to fend off a wounded bug.

Morita MK Carbine

MK55 Rocket Launcher (Nuclear)

MX-90 Hand Grenade
Warning: Do not ever use your teeth to remove the pin of a grenade, unless your name is Dizzy.

Doc's Time Travel Machine (Delorean)
Who doesn't remember the Delorean from Back to the Future? I wanted a car just like this as a kid. Of course, I also wanted the time circuits and fusion reactor installed as well. An iconic prop, and one of the best vehicle props of all time.

Kitt Car
Every kid in the 80's wanted one of these. It talks, taunts, has an ejection seat, goes 300mph. It also has those cool red lights, reminiscent of Cylons from the original Battlestar Galactica.

BSG Colonial Military Pistol
Used in the 2004 miniseries, and the first season, these handguns were modified from a revolver, and had two barrels.

BSG Colonial Military Pistol-Version 2
This is the second version of the Colonial pistol that replaced the one from the first season. It is a FN Five-Seven with an attached second barrel, which houses an explosive projectile.

Vektor CP1
This South African handgun has been used in multiple sci-fi movies and television series. It has a unique look, which makes it ideal as a prop.

HK MP7A1
This Sub-machine gun was used by military and civilian resistance fighters.

HK UMP
This SMG was used by Anders and some security forces.
You'll notice Kara Thrace has some weapons of her own. She is holding two Sa. Vz.61 Scorpion automatic pistols.

Beretta CX4 Storm
These carbines are used by the Colonial Marines as well as some other BSG personnel for most of the series.

Holy Shotgun
Constantine's Holy Shotgun looks completely customized. It has a nice rotary magazine, holy ammunition, and it looks really shiny. I wish I could tell you more about the weapon, but you should really see it in action by watching the movie.

Blade's Blade
Here's Blade, on his bike, with his sword from the first movie.

Blade's Pistol
Blade uses this pistol against the horde of infected vampire mutants. It's a HK USP with a target barrel, and an attachment to the front. There's also a light under the barrel.

Blade's SMG
Blade uses this SMG to take out some vampires. It's a Mac-10 with a heavily rebuilt front end.

Reinhardt's Bladed Pistol
I'm not sure what the official title of this gun is, but it's a Beretta 92-FS with a laser sight, extended barrel, and a curved sharp blade attached to it. Mean looking gun.

Reinhardt's Shotgun
Reinhardt has a light attached to this Remington 870 Marine shotgun. It also has what look like short stakes attached to it, perhaps to double as a melee weapon, much like his pistols.

Nyssa's Skorpions
Nyssa actually has two SA Vz. 61 Skorpion SMGs. Other than a couple of attached lights, they look unmodified.

Chupa's Desert Eagle
Chupa is all too happy to point his IMI Desert Eagle at Blade. The Desert Eagle is a favorite among prop masters for it's size. It shows up really well on the screen.

Asad's M-16
Asad has an M-16 with a grenade launcher attachment. Chupa also has an M-16, with a flashlight attached, and a high capacity magazine.

Snowman's Gear
Snowman seems to be wearing a variant of Japanese Samurai armor on his chest, and wielding a katana and wakizashi.

Foosh Gun
Don't ask me why this was called the 'foosh' gun, but that's the prop title. It's a laser gun, used by a few characters in The 6th Day. I liked it the first time I saw it, and I hope it shows up somewhere in a different movie.

Helicopter
Schwarzenneger's character is a pilot, and he gets to fly this awesome futuristic helicopter.

As a Trek fan, I know the communicator paved the way for today's cell phones (especially the soon-to-be defunct Nextel) and the communication slate Kirk always signed off was the precursor for today's iPad.
That said, gimme an M240-Gulf anytime you want to unleash a world of hurt on someone (human or otherwise) hoo-ah!